1. Field of the Invention
This invention relates to a thermal neutron detector the most elemental component of which is a 10B-lined straw tube which can be applied in multiple applications including neutron radiation survey and neutron imaging. The detector is also capable of counting gamma radiation alone or simultaneously with neutron counting.
2. Description of the Related Art
Neutron scattering is a very valuable technique which is critically important to materials science and structural biology applications. Neutron scattering is an important source of information about the atomic positions, motions, and magnetic properties of solid materials. As a beam of thermal neutrons is directed at a target material some neutrons will interact directly with the atomic nuclei of such material and “bounce” away at various angles related to the atomic arrangements that define the structure of the target material. This behavior is referred to as neutron diffraction, or neutron scattering.
With appropriate detectors one can count the scattered neutrons, measure their energies and the angles at which they scatter, map their final position and thereby calculate the atomic positions of the atoms in the target material that caused such scatter pattern. In this way one can determine details about the nature of target materials ranging from liquid crystals to superconducting ceramics, from proteins to plastics, and from metals to micelles to metallic glass magnets. The knowledge gained with respect to such materials has resulted in far-reaching advances in engineering, pharmaceutical and biotechnology industries, to name a few.
New facilities for neutron generation at much higher flux (neutron events/second), such as the Spallation Neutron Source (SNS) facility due for completion at Oak Ridge in 2006, will greatly enhance the capabilities of neutron scattering. The benefits offered by superior neutron scattering techniques extend to many fields and include, for example, development of improved drug therapies and materials that are stronger, longer-lasting, and more impact-resistant. However, in order to fully realize this greater neutron scatter potential these higher flux rates must be met with improved neutron scatter detection capabilities; particularly higher count rate capability in large area size detectors, while maintaining practicality.
The SNS facility will enhance the available thermal neutron flux by at least an order of magnitude above that now achievable at any other neutron science facility. This higher neutron beam intensity, together with time of flight energy discrimination provided by pulsed operation of the SNS facility, will facilitate unprecedented capabilities, which will be exploited in more than 18 experiment stations (http://www.sns.gov/). The markedly increased deliverable neutron flux imposes extreme rate requirements on the neutron scattering detectors in many of these facilities, which cannot now be met without fundamental detector improvements.
Although present 3He pressurized area detectors can provide needed spatial resolution, sensitivity and gamma ray discrimination, this 3He detector technology cannot now achieve the needed high rate operation, which, for many SNS detector stations, can reach rates over 108 neutrons/sec, for detectors of 1 m2 in area. The expansive scope of the experimental stations of the SNS has also pushed the area requirements of neutron detectors to many square meters. The high resolution powder diffractometer facility, for example, calls for 47 m2 of detectors. Achieving such large areas for neutron detection with pressurized 3He technology is extremely expensive and difficult because of the complexity of the pressure containing structures required for 3He neutron detection. Current neutron detectors, such as 3He tubes, have significant practical limitations, including high cost, substantial weight and bulkiness, and are dangerous in portable use due to the high pressure of 3He they require.
A compelling need exist for alternative detectors with more favorable characteristics.